Klystron tube having feedback means and a control lens



R. F. FRENCH July 29, 1969 KLYSTRON TUBE HAVING FEEDBACK MEANS AND A CONTROL LENS Filed Jan. 12, 1966 4 Sheets-Sheet 1 FIG.

FIG. 2

INVENTOR. ROGE R F. FRENCH R. F. FRENCH 3,458,750

KL YSTRON TUBE HAVING FEEDBACK MEANS AND A CONTROL LENS July 29, 1969 4 Sheets-Sheet 2 Filed Jan. 12, 1966 INVENTOR. ROGER F-FRENCH m/ wx 1/ FIG. 4

KLYSTRON 'rusm HAVING FEEDBACK MEANS AND A CONTROL LENS R. F. FRENCH July 29, 1969 4 Sheets-Sheet 5 Filed Jan.

INVENTOR. ROGER F FRENCH July 29, 1969 R. F. FRENCH 3,458,750

KLYSTRON TUBE HAVING FEEDBACK MEANS AND A CONTROL LENS Filed Jan. 12, 1966 4 Sh eets-Sheet 4 FIG. 7

United States Patent US. Cl. $15-$44 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a klystron tube and, more particularly, to a tube of that type having a control lens formed of a thin metallic coating on a ceramic support and receiving an electrical charge through a lead which also acts as a feedback device.

The advantages of cooking with microwave radiation in contrast to other forms of cooking have been recognized for some time. Among these advantages are the speed in which cooking takes place and the absence of heating of the vessels in which the cooking takes place. Heretofore, however, the cost of even a small microwave oven has been so high that very little use of this technique has been possible for domestic cooking. Even in the case of commercial cooking, where, under certain circumstances, the high cost of the oven can be justified, maintenance has always been a major problem. Forone thing, the basic magnetron tube, which (in earlier models) generated the microwave radiation, wears out rapidly and represents a very costly item to replace. Also, the basic elements of the oven are difficult to maintain in a precise geometric relationship and, for that reason, the distribution of the microwave energy may change greatly with warpage and denting of the oven material and with aging of the magnetron. In many case, the prior art ovens have been very unsafe. Furthermore, many elements are required in the electrical circuitry and, therefore, produce a rather bulky oven for a given cooking volume. These and other difliculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a microwave oven which is inexpensive to manufacture, which is capable of a long life of useful service with a minimum of maintenance.

Another object of this invention is the provision of a microwave oven which maintains a good cooking pattern, despite the wear and tear of normal use.

It is a further object of the invention to provide a microwave oven including an inexpensive klystron tube which is capable of a long life of useful service.

A still further object of this invention is the provision of a klystron tube of novel contruction, which is relatively inexpensive to manufacture and which has extermely long life.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, maybe best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of a microwave oven embodying the principles of the present invention,

FIG. 2 is a further perspective view of the invention with an outer cabinet removed;

FIG. 3 is a further perspective view of the oven showing the inner construction particularly well,

3,458,750 Patented July 29, 1969 "ice FIG. 4 is a perspective view of the oven as observed from the rear side,

FIG. 5 is a perspective view of a klystron tube forming a part of the present invention,

FIG. 6 is a central perspective view of the tube,

FIG. 7 is a perspective view of a lens used in the klystron and forming'part of the invention,

FIG. 8 is a front elevational view of the lens,

FIG. 9 is a sectional view of the klystron taken on the line IXIX of FIG. 6.

Referring first to FIG. 1, wherein are shown the general features of the invention, it can be seen that the microwave oven, indicated generally by the reference numeral 30, consists of a cabinet 31 enclosing an oven chamber and having a door 32. Above the door is a control panel 33 having an ON-OFF switch 34 and a timer control knob 35. In the center of the door 32 is a grill 36. At the free edge of the door it is provided with a handle 37 which operates a latch cooperating with a latch opening 38. Within the oven is a cooking chamber 39 containing an article 41 to be cooked which, for the purposes of illustration, is shown as a cup of instant coffee in its saucer.

FIG. 2 shows the oven with the cabinet 31 removed. The cooking chamber 39 is defined by a top wall 42, a bottom wall 43, a side Wall 44, a side wall 45, and a rear wall 46. FIG. 2 shows the rear side of the door 32 and the latch 47 extending therefrom. Fastened to the outer surface of the rear wall 46 is a blower 48. Under the blower adjacent the rear wall is located a transformer element 49 and fastened over the top wall 42 is a wave guide 51. The walls 42, 43, 44, 45, and 46 which form the cooking chamber 39 are fastened together to give a strong, rigid relationship with a minimum of electrical interference by fasteners and other projections into the chamber 39. Each edge of a wall at its intersection with another wall is provided with an extension or flange, either in the same plane as the wall or at a right angle thereto. Each flange lies against a corresponding extension of the wall which it intersects. Two flanges are fastened together by a row of rivets in which the rivets are closely spaced relative to one another in a straight line, the line being spaced a substantial distance away from the actual corner of the chamber.

An example of the way this is done appears in FIG. 2 at the intersection of the side wall 45 and the rear wall 46. The rear wall 46 is provided with an extension 52 which is in the same plane as the rear wall 46, while the side wall 45 is provided with an extension or flange 53 which extends at a right angle to the plane of the side wall 45. The extension 52 and the flange 53 are fastened together by a row of rivets 54 which lie in a straight line parallel to the surface of the side wall 45 and spaced from its plane. The row of rivets 54 are spaced a substantial distance away from the intersection of the side wall 45 and the rear wall 46. Although it cannot be seen in FIG. 2, the corner formed by the side wall 45 and the rear wall 46 on the inside of the oven chamber 39 is uninterrupted by fasteners or other projections and, therefore, forms a perfect corner, so far as interference with the microwave pattern is concerned. All of the other corners of the oven are formed in a similar way making use of flanges and extensions and rows or rivets spaced away from the corner so that the sides are formed into a rigid box which is not easily deformed along the front of the oven. Overlying the normal, closed position of the door 32 is a vertical panel 55, behind which are baffles 56 for a purpose to be explained. Underlying the bottom wall 43 and supporting the oven is a channel 57 and a channel 58 (see FIG. 4), between which lies a passage 59 constituting an inlet air duct. The transformer element 49 is mounted on and extends between these two channels. As is evident in FIG. 2, the grille 36 consists of a sheet metal with small circular apertures, which sheet metal is riveted in a large opening in the central portion of the door.

FIG. 3 shows particularly well the interior of the oven chamber 39. Located centrally of the top wall 42 is an aperture 61 through which extends a vertical antenna 62. Rotatably mounted on the bottom end of the antenna as it extends downwardly into the chamber 39 is a diffuser blade 63. Extending through the side wall 44 are several apertures 64, while a similar set of apertures 65 extend through the upper part of the rear wall 46.

FIG. 4 shows particularly well the general features of the invention as viewed from the rear with the cabinet 31 removed. Mounted on the top wall 42 is the wave guide '51. At the front of the oven extends the panel 55 and behind it the baffles 56. The exterior of the apertures 64 can be seen in this view, as can be seen the manner in which the air passage 59 arrives from the front of the oven between the channels 57 and 58. As is evident in this view, the blower 48 is of the centrifugal type having a central inlet opening 66 wherein can be seen the blades which are driven by a central motor 67. The blower is provided with an outlet duct 68 which extends horizontally with its opening facing to the left in FIG. 4. Mounted on the rear wall 46 of the oven is a klystron 69, which will be described more fully hereinafter. Furthermore, it can be seen in this view that the rearward end of the wave guide 61 is open and is provided with a closure in the form of a choke 71. The transformer element 49 is shown as consisting of two bars 72 and 73 which are mounted across the channels 57 and 58 in spaced parallel relationship. Fastened to the top of the bars extending transversely across is a short channel member 74 which carries a chassis 75 in which are mounted four rectifiers 76. Also mounted on the chassis channel 74 is a capacitor 77. At the other end of the transformer element 49 mounted on the bar 72 and 73 is a power relay 78. A channel 79 is bolted to the bar 73 and extends vertically upwardly to be bolted to and support the outboard end of the motor 67.

FIGS. and 6 show the details of the klystron 69. It is provided with a tubular copper body 81, to one end of which is attached a cathode assembly 82. At the other end are mounted a series of copper fins 83 whose outer ends are fastened to and enclosed by a shroud 84. Also mounted in the other end and acting as a closure therefor is a cylindrical block 85 also formed of copper and provided in its axial inner portion with a stepped recess 86. Close to the said other end and extending at a right angle to' the axis of the body 81 is a nickel tube 87 at the other end of which is fastened a ceramic dome 88.

As is evident in FIG. 5, the fins 83 and the shroud 84 are omited in the area surrounding the tube 87 and a mounting plate 89 is coextensive with the fins and the shroud and extends from one edge of the shroud to the other for the purpose of mounting the klystron. Apertures 91 extend through the plate 89 for that purpose and are normally fastened to the bottom wall of the wave guide 51 so that the dome 88 extends upwardly into the wave guide, as is evident in FIG. 4. The tube 93 is fastened to and extends out of the housing 81 adjacent the cathode unit 82 for the purpose of evacuating the tube during the original manufacture and this tube is pinched or closed off in the usual way.

The cathode unit 82 consists of a tube 92 formed of nickel which is fastened to the end of the body 81 as an extension thereof and carries at its outer end a ceramic disc 94. Mounted on the inner surface of the disc 82 by means of metal rods 95 is the cathode which is of generally cylindrical form coaxial with the tubular housing 81 and it is provided with a spherical emission surface 97 facing toward the end of the housing 81. Enclosed in the cathode is a heating filament 98 from which are connected through the ceramic disc 94 by two leads 99 and 101. A third lead 102 extends through the disc and is electrically connected to a sheet metal focusing ring 100 which is coaxial with the cathode 96 which extends between the surface 97 and the end of the body 81. Also connected to the lead 102 is a lead 103 for a purpose to be explained more fully hereinafter.

Extending across the housing 81 is a wall 104 having a central aperture in which is mounted an electrode ring 105 having a bore 106 which is coaxial of the housing. Spaced from the wall 104 and parallel to it is a second wall 107 having a central aperture carrying an electrode ring 108. Thus, a double-reentrant resonant cavity is formed. The ring 108 has a bore 109 which is coaxial of the housing 81. Spaced from the wall 107 and parallel thereto and generally lying in the plane of the edges of the fins 83 is a third wall 111 having a central opening in which is carried an electrode ring 112 having a bore 113 which is coaxial of the housing 81. Extending across the housing 81 is a fourth wall 114 which is parallel to the wall 111 and spaced therefrom a distance somewhat shorter than the distance between the Wall 104 and the wall 107 or the distance between the wall 107 and the wall 111. The fourth wall 114 is provided with a central aperture carrying an electrode ring 115 whose central bore 116 is also coaxial of the housing 81. Finally, the surface 117 of the block 85 faces toward the wall 114 and, as has been described, is furnished with a recess 86 which is a series of cylindrical bores of diminishing size. Fastened to the surface 117 is a ring 118 having a bore 119 which is coaxial of the housing 81 and coaxial of the recess 86. A bore 106 of the ring 105 is of frusto-conical form and has its largest diameter at the end facing toward the cathode 96. The bore 109 of the ring 108 is provided at one end with a cylindrical portion 121 at the end which faces toward the ring 105 and a conical portion 122 at the end which faces toward the ring 112, the smaller end of the frusto-conical portion 122 being toward the ring 112. Finally, an annular groove 123 is provided in ring 121 to provide a means of adjusting the gap spacings after the tube is brazed.

The walls 104 and 107 define with the inner surface of the housing 81 an annular chamber 124. The walls 107 and 111 define with the inner surface of the housing 81 an annular chamber 125. The Walls 111 and 114 define a chamber 126; the wall 114, the surface 117, and the inner surface of the housing 81 define a chamber 127. The chambers 124, 125, and 127 thus form reentrant-cavity resonators. Fastened in the wall 114 near its outer periphery is a feed rod 128 which extends longitudinally a short distance and then is bent at a right angle to extend coaxially through the tube 87 into the dome 88. The dome is provided with a main inner bore 129 and then is provided with a short counterbore 131 at its outer end which is of exactly the proper diameter to hold firmly the free outer end of the rod 128, the rod being coaxial of the main bore 129. The outer surface of the dome 88 is provided with a light metallized coating and, by this means, it is then brazed into the inner surface of the tube 87.

Extending transversely of the housing 81 and located midway between the wall 111 and the wall 114 is a focusing lens 132 which is electrically connected to the lead 103 extending longitudinally through the tube. The lead extends through suitable apertures 133, 134, and in the walls 104, 107, and 111, respectively. A quartz sleeve 136 fits snugly within a copper tube 137. The apertures 133 and 135 in the walls 104 and 111, respectively, are of such a size that the tube 137 can be brazed to them and held there against movement. The aperture 134 is substantially larger than the outside diameter of the tube 137 so that an annular space is defined between the surface of the aperture 134 and the outer surface of the tube 137. Assemblage of the lead 103 within the quartz sleeve 136 and the copper tube 137 serves the function of not only providing a suitable electrical charge on the lens 132 but also furnishing a microwave feedback from the chamber 125 to the chamber 124 to provide oscillation.

FIG. 9 shows the manner in which the lead 103 fits tightly in the quartz sleeve 136. It also shows the way in which the sleeve 136 fits snugly in the copper tube 137. In FIG. 9 it is also evident that a substantial annular space exists between the outer surface of the tube 137 and the surface of the aperture 134 in the wall 107.

FIGS. 7 and 8 show the details of construction of the focusing lens 132. The lens is provided with a main ceramic disc 138 having, as is evident in FIG. 6, a diameter substantially less than the inner diameter of the tubular main body 81. Adjacent the outer periphery of the disc and spaced many degrees apart are three apertures 139, 141, and 142 which, by means of a rivet and a spacing sleeve surrounding the rivet, serve to fasten the disc to the wall 111. The disc is provided with a central coaxial circular aperture 143 whose surface is provided with a thin coating providing a focusing electrode 144. Not only is the surface of the aperture 143 coated, but the radial surface of the disc on both sides around the aperture is also similarly coated, as is evident in FIG. 6. Extending away from the band of coating and extending around the aperture is a radial strip 145 which extends outwardly to a point at the outer periphery of the disc. The outer periphery is provided at that point with a radial bore 146 in which the end of the lead 103 is mounted and electrically connected to the coating. In other words, the ceramic disc 138 acts as a mechanical support for a thin electrode 144. The electrode is spaced an appropriate distance from any other metallic elements of the tube, particularly the wall 111. This provides good insulation, permitting high voltages to be applied in a minimal space without voltage breakdown.

The operation of the apparatus will now be readily understood, in view of the above description. The article 41 is placed in the cooking chamber 39 and the door 32 is closed. When the door is closed, the rod 47 extends through the opening 38 and the aperture 233 in the flange 217. When the handle is in the horizontal position shown in FIG. 1, the peg 234 is vertical and goes through the aperture readily. Then, the operator turns the handle down to its downwardly-extending condition so that the peg 234 extends horizontally and strikes the actuator of the interlock switch 235. The ON-OFF switch 34 is moved to the ON position. The timer control knob 35 has been previously set to give the proper amount of time for the oven to be operative.

Referring to FIGS. 5 and 6, the klystron, once the filament 93 has been heated up, permits the surface 97 of the cathode 96 to emit a stream of electrons which is focused not only by the spherical shape of the surface 97 but by the focusing ring 100 and the stream proceeds longitudinally of the klystron. It passes through the rings 105 and 108. The dimensions of elements are selected so that the minimum beam diameter appears at the gap between rings 109 and 112. It passes through the bore 113 of the ring 112, through the coating 144 of the electrostatic electrode lens 132, and then through the bore 116 of the ring 115. Because of the influence of the microwave field on the wall 114 to which the rod 128 is attached, microwave energy is presented to that rod and passes along the rod to its outer end lying within the bore 131 of the dome 88. Stray electrons are captured by the ring 118 proceeding through the bore 119 and ending up in the block 85 and the stepped bore 86. The lead 102 is not only connected tothe focusing ring 100 but also to the lead 103, which is connected to the metallized coating 144 of the lens 132. This high voltage lead is suitably isolated by the quartz sleeve 136 and, of course, the coating 144 is supported on the ceramic disc 138. At the same time, the quartz sleeve 136 is mechanically protected by the copper tube 137. This tube also acts to lead energy from the chamber to the chamber 124 through the aperture 134 in the wall 107 and causes the klystron to oscillate by virtue of the coupling between cavities 125 and 124; it, therefore, serves a dual purpose. Any heat absorbed in the body 81 of the klystron, the rings 105, 108, 112, 116, and 118, and in the copper block 85 passes outwardly through the fins 83. Air passes over these fins at high velocity within the shroud 84 to maintain the klystron within satisfactory temperature limits.

While most of the copper parts of the klystron body are fastened together by silver brazing, it is preferred to attach the dome 88 to the tube 87 by copper brazing. This forms a sub-assembly which is then silver brazed to the main body 81. When the tube is tested for vacuum and for leakage, the most frequent area of leakage is in the connection between the dome 88 and the tube 87. According to the present construction, if the klystron grooves to have a leak in this area, it is not necessary to throw the entire construction away at this late stage in manufacture. It is only necessary to remove the top of tube 87 and the dome 88 as a unit and replace it with a new unit, rebrazing the new shorter sub-assembly to the stub of old tube 87 using silver for brazing. This procedure obviates one of the manufacturing problems experienced in the prior art.

The arrangement for mounting the high voltage disc 132 is quite interesting. Because of the nature of the electrical element, it is only necessary that a metallic coating 144 be applied to control the stream of electrons. However, this carrying member for the voltage must be rigidly supported. The concept of using the ceramic disc which is connected to the wall 111 (which, in turn, is at ground potential) by fastenings at the extreme periphery of the disc, while the lead enters from the edge of the disc at a point separated from the attachment points, assures that the support connections are as far from the high voltage connections as possible. At the same time, the ceramic disc 138 is very rigid and holds the geometric relationship of the coating to the rest of the elements in the klystron.very accurately and for a long length of time. In the drawing, of course, the coating 144 is shown as having substantial thickness but, of course, in actuality, it is quite thin. This design provides the necessary insulation and provides a more compact line assembly providin g higher performance in the klystron.

Referring to FIGS. 1 and 3, the microwave energy arrives in the cooking chamber 39 through the antenna 62. The flow of air from the aperture 65 causes the diffuser blades 63 to rotate in the Teflon bearing members 243 and 244 by which the hub 242 is mounted on the vertical antenna 62. The blades operate to spread the microwave pattern to all parts of the cooking chamber to prevent concentrations of energy at any given point, so that the article 41 may be placed in almost any part of the cook ing chamber and receive equal treatment. If the article 41 is extremely large, as in the case of a pie or a large piece of meat it, of course, is undesirable that any particular portion receive more energy than another portion and the diffusion resolves this difficulty.

In FIG. 2, it can be seen that the type of construction used with the oven renders it very rigid and provides it with a geometrically accurate inner surface, despite the fact that it is formed of thin aluminum sheet. By using the flanged and riveted construction, the shape of the chamber 39 remains constant, so that the microwave pattern provided by the antenna always operates in the same manner, even though the oven has been subjected to considerable use. In addition, there are no fasteners or rivets at the corners of the interior of the chamber to upset the microwave pattern.

The details of construction of the present klystron result in an amplifier-type device using the combination of an oscillator, an amplifier, and a linear-beam type klystron. Three cavities are used with an oscillating circuit between the first and second cavity. The klystron is electrostatically focused by means of the lens electrode which is connected to the cathode. The klystron uses the multipactor effect in the second gap to control amplitude of oscillation; this usually deleterious effect is now used constructively. The use of the feedback connection between the first two cavities by means of a copper tube with a quartz insulating tube inside to carry the connection between the lens electrode and the cathode is a simple multi-functional construction.

A serial-type control for the voltage for the tube provides a voltage divider which compares the voltage to a Zener reference diode. The difference is amplified by transistors to control the current in a saturable reactor. This results in an effective way in the control of the output voltage of the power supply. In connection with the klystron, the particular output terminal arrangement provides a mechanical support for the tube and provides for good cooling of the seal, because the tube and the dome lie in the direct flow of air from the fan. The particular arrangement of parts permits a good electrical contact to be made to the output circuit and permits the use of copper for a brazing material, while still permitting the use of copper for the center conductor. This results in low microwave losses and a lower cost of assembly, since, if the tube is not tight the first time, the construction permits the output tube to be cut off and a new one added, thus salvaging the tube.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, What is claimed as new and desired to secure by Letters Patent 1. In a microwave oven, a klystron, comprising:

(a) an elongated tubular housing,

(b) a cathode located at one end of the housing for providing a stream of electrons passing longitudinally of the housing,

(c) a series of partitions extending transversely of the housing and dividing it into a plurality of cavities, each partition having an aperture concentric with the centerline of the housing and a lens mounted in the aperture through which said stream passes, the partitions and apertures being at ground potential,

(d) a control lens located between two of the aforementioned apertures,

(e) a lead extending longitudinally of the housing from the control lens to the exterior of the housing to carry a potential other than ground to the lens,

(f) a ceramic tube surrounding the lead, and

(g) a metal tube surrounding the ceramic or quartz tube and supporting the same, the tube extending through apertures in a plurality of the partitions along a line parallel to and spaced from the centerline of the housing, the aperture through the partition separating two of the cavities being substantially larger than and separated from the exterior surface of the tube, the tube fitting tightly in the apentures in the partitions on the other sides of the said two cavities, whereby the tube acts as a feedback device between the said two cavities.

2. In a microwave oven, a klystron, comprising:

(a) an elongated tubular housing,

(b) a cathode located at one end of the housing for providing a stream of electrons passing longitudinally of the housing,

() a series of partitions extending transversely of the housing and dividing it into a plurality of cavities, each partition having an aperture concentric with the centerline of the housing and a drift tube mounted in the aperture through which said stream passes, the

housing, partition, and apertures being at ground potential,

(d) a control lens located between two of the aforementioned apertures, the lens consisting of a ceramic disc supported in the housing by connections adjacent the outer periphery of the disc, the disc having a central aperture, a metallic coating in the form of a ring on the surface of the disc adjacent the aperture and forming a narrow regular path to the periphery of the disc,

(e) a lead extending longitudinally of the housing from the control lens to the exterior of the housing to carry a potential other than ground to the lens,

(f) a ceramic tube surrounding the lead, and

(g) a metal tube surrounding the ceramic tube and supporting the same, the tube extending through apertures in a plurality of the partitions along a line parallel to and spaced from the centerline of the housing, the aperture through the partitions separating two of the cavities being substantially larger than and separated from the exterior surface of the tube, the tube fitting tightly in the apertures in the partitions on the other sides of the said two cavities, whereby the tube acts as a feedback device between the said two cavities.

3. In a microwave oven, a klystron, comprising:

(a) an elongated tubular housing,

(b) a cathode located at one end of the housing for providing a stream of electrons passing longitudinally of the housing,

(c) a series of partitions extending transversely of the housing and dividing it into a plurality of cavities, each partition having an aperture concentric with the centerline of the housing and a drift tube mounted in the aperture through which said stream passes, the partitions and lenses being at ground potential,

(d) an output rod associated with the other end of the housing and having a free end extending transversely of the housing externally thereof,

(e) a ceramic dome fastened to the housing and extending laterally thereof, the dome having an internal cavity opening into the housing and receiving the rod, a portion of the cavity being formed to receive the said free end of the rod for the location and support thereof,

(f) a control lens located between two of the aforementioned lenses,

(g) a lead extending longitudinally of the housing from the control lens to the exterior of the housing to carry a potential other than ground to the lens,

(h) a quartz tube surrounding the lead, and

(i) a metal tube surrounding the tube and supporting the same, the tube extending through apertures in a plurality of the partitions along a line parallel to and spaced from the centerline of the housing, the aperture through the partitions separating two of the cavities being substantially larger than and separated from the exterior surface of the tube, the tube fitting tightly in the apertures in the partitions on the other sides of the said two cavities, whereby the tube acts as a feedback device between the said two cavities.

4. In a microwave oven, a klystron, comprising:

(a) an elongated tubular housing,

(b) a cathode located at one end of the housing for providing a stream of electrons passing longitudinally of the housing,

(0) a series of partitions extending transversely of the housing and dividing it into a plurality of cavities, each partition having an aperture concentric with the centerline of the housing and a drift tube mounted in the aperture through which said stream passes, the housing, partitions, and lenses being at ground potential,

(d) an output rod associated with the outer end of the housing and having a free end extending transversely of the housing externally thereof,

(e) a ceramic dome fastened to the housing and extending laterally thereof, the dome having an internal cavity opening into the housing and receiving the rod, a portion of the cavity being formed to receive the said free end of the rod for the location and support thereof,

(f) a control lens located between two of the aforementioned apertures, the lens consisting of a ceramic disc supported in the housing by connections adjacent the outer periphery of the disc, the disc having a central aperture, a metallic coating in the form of a ring on the surface of the disc adjacent the aperture and forming a narrow radial path to the periphery of the disc,

(g) a lead extending longitudinally of the housing from the control lens to the exterior of the housing to carry a potential other than ground to the lens,

(h) a quartz tube surrounding the lead, and

(i) a metal tube surrounding the ceramic tube and supporting the same, the tube extending through apertures in a plurality of the partitions along a line parallel to and spaced from the centerline of the housing, the aperture through the partition separating two of the cavities being substantially larger than and separated from the exterior surface of the tube, the tube fitting tightly in the apertures in the partitions on the other sides of the said two cavities, whereby the tube acts as a feedback device between the said two cavities.

5. In a microwave oven, a klystron, comprising:

(a) an elongated tubular housing,

(b) a cathode located at one end of the housing for providing a stream of electrons passing longitudinally of the housing,

(c) a series of partitions extending transversely of the housing and dividing it into a plurality of cavities, each partition having an aperture concentric with the centerline of the housing and a drift tube mounted in the aperture through which the said stream passes,

(cl) an output rod associated with the other end of the housing and having a free end extending transversely of the housing externally thereof,

(e) a ceramic dome fastened to the housing and extending laterally thereof, the dome having an internal cavity opening into the housing and receiving and supporting the rod, a portion of the cavity being formed to receive the said free end of the rod for the location and support thereof, the dome being mounted in the end of an elongated sleeve extending laterally of the housing, the dome having a metallic coating by which it is brazed to the sleeve,

(f) a control lens located between two of the aforementioned apertures, the lens consisting of a ceramic disc supported in the housing by connections adjacent the outer periphery of the disc, the disc having a central aperture, a metallic coating in the form of a ring on the surface of the disc adjacent the aperture and forming a narrow radial path to the periphery of the disc, the metallic coating consisting of a ring around the aperture on either side thereof joined by a tube covering the surface of the aperture itself, and

(g) an electrical lead from the exterior of the housing to the said path to impress upon the said coating a potential other than ground.

References Cited UNITED STATES PATENTS 2,498,673 2/1950 Goudet et al 315--5.34 2,512,887 6/1950 Davies et al. 3155.44 X 2,543,011 2/1951 Gibson 315-5.44 3,267,322 8/1966 Disman 315--5.34

HERMAN KARL SAALBACH, Primary Examiner S. CHAT MAN, JR., Assistant Examiner U.S. Cl. X.R. 

